Story highlights

Washington (CNN)A video emerged Friday that purportedly shows a US payment of $400 million worth of cash delivered to Iran on the day Tehran released several American prisoners in January.

CNN cannot authenticate the newly surfaced video, which was part of an Iranian documentary that first aired in January and shows the money on pallets in a warehouse. But the latest wrinkle is bound to fuel critics of the administration who have accused Obama of providing ransom to the Iranian government in exchange for the release of four US prisoners. A fifth American was released separately.

The Obama administration has vehemently denied any connection between the cash delivery and the release of the American prisoners.

"We announced these payments in January. Many months ago. They were not a secret," Obama told reporters at the Pentagon Thursday.

"It was not a nefarious deal," Obama said, adding, "We do not pay ransom for hostages."

Read More

However, US officials, while denying a connection, have publicly admitted that the timing of the two transactions -- US prisoners leaving Iran as hundreds of millions of dollars arrived -- involved problematic optics.

Others have raised questions as to whether the release of the Americans was conditional upon the payment of the money and whether it encourages more questionable arrests by Iran of Americans living there.

A US official told CNN that is was "unknowable" whether Iran would have freed the prisoners without the settlement payment.

And an Obama administration official insisted Saturday that the release of Iranian nationals from US prisons as part of the swap for the incarcerated US citizens was "not conditional on any payment. Their release was conditional on the series of commutations and pardons (the Department of Justice) spoke to at the time."

Trump walks back video claim

The revelation came hours after Republican presidential candidate Donald Trump walked back an earlier claim that he had seen tape of the delivery, acknowledging Friday morning that the footage he watched was actually the American captives arriving in Geneva.

Trump's repeated reference to having seen the video was widely questioned, since at the time no such footage had been identified.

Trump initially claimed to have seen video of the cash being unloaded from a US aircraft in Iran and repeated the assertion on Thursday even though a campaign aide had told The Washington Post earlier that it was actually footage of a different event.

Trump then said via Twitter Friday that he had only seen the American prisoners arriving in Geneva, Switzerland.

The plane I saw on television was the hostage plane in Geneva, Switzerland, not the plane carrying $400 million in cash going to Iran!

Democratic vice presidential candidate and Virginia Sen. Tim Kaine slammed Trump for his earlier claim, saying, "I have no idea what he's talking about. It (the video) doesn't exist. He might be thinking about Iran-Contra from like 35 years ago or something like this," while appearing on CBS' "This Morning."

The footage Trump referred to featured a plane, while the video from the Iranian documentary shows only the pallets stacked with cash, according to Iranian state television.

The January deal, well publicized at the time, was officially part of a $1.7 billion settlement involving a dispute dating back to a 1970s-era failed arms deal with the government of the Shah of Iran. US officials have said that the settlement and subsequent release of frozen Iranian assets was agreed to in order to avoid a potentially more costly international arbitration.